In this paper, we consider the three-hop MTMO relaying systems, based on the amplify-and-forward (AF) protocol, where there arc two relay nodes both of which are equipped with multiple antennas, over Gaussian broadcast channels. We also consider that the base station (BS) broadcasts the signals to multiple distributed users via two relay nodes, that is, three hops, using a zero-forcing dirty paper coding (DPC). We propose three different relaying strategics depending on adopting the power loading from the antennas of each relay node. We calculate both the lower and the upper bounds of the sum capacity of the different relaying strategics we proposed and compare these lower and upper bounds with the sum capacity of the decodc-and-forward (DF) protocol based system. In our paper we derive the optimal power allocation at both relay nodes and the BS by using the geometric programming. The simulation results show that our proposed relaying strategics can achieve a similar sum capacity with the upper bound of the three-hop multiuser MIMO relaying system, and these outperform the two-hop multiuser MTMO relaying system proposed in  or the multiuser MIMO system without relays in terms of the sum capacity.